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NRC Postdoctoral Opportunities

RESEARCH OPPORTUNITIES

DNA Transport in Single Nanopores

We are studying the mechanism by which DNA partitions into and threads through single nanometer-scale pores. This experimental and theoretical effort focuses on understanding how genetic information is exchanged between organisms (e.g., between virus and host cells or between bacteria) and on adapting single nanopores for novel biological and biotechnological applications. It was recently shown that the interaction between polymers and a single nanopore provides the physical basis of a multi-analyte sensor. Work is also underway to determine whether this system could be used as tool to rapidly sequence long strands of DNA and RNA.

Contact: John Kasianowicz, 301-975-5853

Electrical and Optical Characterization of Semiconductors and Devices

Research focuses on understanding the electronic, optical, and magneto-optical behavior of semiconductor materials and devices. Areas of interest include the role of impurities and native defects in bulk crystals, and novel and useful properties induced by quantum confinement in reduced dimensional structures (heterostructures, quantum wells, superlattices, and quantum wires and dots). A broad range of optical techniques is available for reflection, transmission and absorption, and modulation spectroscopy; photoluminescence and photoluminescence excitation; Raman and resonant-Raman scattering; spectro-scopic ellipsometry, and surface photovoltage. A wide variety of electrical and magnetotransport techniques are also utilized to characterize the electronic properties. Emphasis is placed on understanding fundamentals and technologically relevant properties as well as developing accurate measurement techniques.

Contact: David Seiler, 301-975-2054

Electrical Overlay- and CD-Metrology Development for Characterization of Advanced Lithography Instruments for Interconnect Applications

Projected critical dimension (CD) and overlay control-tolerances for new generations of ICs are reducing metrology uncertainty tolerance down to the several-nanometer region. However, the development of CD and overlay metrology standards are not keeping pace with lithographic resolution capabilities of advanced imaging systems. The Enabling Devices and ICs Group seeks individuals interested in conducting further research in (1) the design and optimization of reference materials for scatterometry metrology; (2) noncontact electrical CD-measurement and extraction methodologies; and (3) design, fabri-cation, and certification of CD standards in the range 20 nm to 100 nm. We also encourage applicants with research experience in noncontact/nonintrusive electrical CD extraction and multimode overlay-sensor development for novel CD reference-material implementations. The project is also initiating a study of unique materials and metrology issues associated with copper interconnect for ultra-high speed IC applications.

Contact: Michael Cresswell, 301-975-2072

Functionalizing Semiconductor Surfaces

Combining organic monolayers with semiconductor surfaces is of interest for many differing applications including molecular electronics, sensors, and bio-electronics. Monolayers on semiconductor surfaces take advantage of the increased electrical functionality, chemical and structural robustness, wealth of fabrication knowledge, and present a less disruptive technology compared with monolayers on typically used metal substrates. We are investigating various experimental approaches to form organic monolayers on semiconductor surfaces. The resulting films are characterized by using Fourier-transform infrared spectroscopy, spectroscopic ellipsometry, contact angle measurements, and atomic force microscopy. Key aspects of this work involve examination and optimization of alternative functionalization pathways for monolayer formation and thorough characteriza-tion of the resulting monolayer. More advanced applications include formation of biorepellent monolayers in addition to monolayers specifically tailored to bind differing biological moie-ties.

Contact: Christina Hacker, 301-975-2233

MicroElectroMechanical Systems

The MicroElectroMechanical Systems (MEMS) project focuses on the development of new MEMS-based sensors and actuators for meas-urement applications. It functions in a multidisciplinary environment with collaborations in the NIST laboratories in Chemistry, Materials Science, Physics, Biotechnology, and Building and Fire Research. Current activities in the project include thermal-based elements, mechanically resonant structures, microwave elements, and microfluidic systems. The project is also develop-ing MEMS test structures, test methods, and standards to characterize device properties for device performance and reliability testing. These MEMS-based test structures are being utilized to characterize thin-film properties in mainline semiconductor fabrication processes. We are interested in postdoctoral applications not only from individuals who have specialized in MEMS research but also from individuals of other sci-ence disciplines who wish to learn microfabrication methods and apply their expertise for new measurement applications.

Contact: Michael Gaitan, 301-975-2070

Modeling Advanced Semiconductor Devices for Circuit Simulation

Accurate circuit simulator models for advanced semiconductor devices are required for effective computer-aided design of electronic circuits and systems. However, the semiconductor device models provided in most commercial circuit simulators (e.g., simulation program with integrated circuit emphasis) are based on microelec-tronic devices, and they do not adequately describe the dynamic behavior of advanced semiconductor devices. Therefore, research focuses on the following: (1) physics-based models-for advanced semiconductor devices such as power and compound semiconductor devices; these models are implemented into available circuit and system simulation programs; (2) parameter extraction algorithms-for obtaining model parameters from terminal electrical measurements; and (3) characterization procedures-for verifying the models' ability to simulate the behavior of the devices within application circuits. NIST also works closely with commercial software vendors to make the new models available to circuit design engineers, and has established the NIST/IEEE Working Group on Model Validation to develop comprehensive procedures for evaluating the performance of circuit simulator models.

Contact: Allen Hefner, Jr., 301-975-2071

Molecular Electronics: Electrical Metrology

In Molecular Electronics-a field that is predicted to have important technological impacts on the computational and communication systems of the future-molecules perform the functions of electronic components. We are developing methods to reliably and reproducibly measure the electrical properties of small ensembles of molecules in order to investigate molecular conduction mechanisms. Specifically, we are developing test-structures based on nanofabrication and MicroElectroMechanical Systems processing techniques for assessing the electrical properties and reliability of moletronic molecules. In addi-tion to the complexity of the nanofabrication of test structures, the challenges associated with measuring the electrical properties (such as current-voltage and capacitance-voltage as func-tions of temperature and applied fields) of these small molecular ensembles are daunting. The measured electrical properties will be correlated with systematic characterization studies by a variety of probes and the results used in the validation of predictive models. This task is part of a cross-disciplinary, inter-laboratory effort at NIST whose overall role is to develop the measurement science that will enable molecular electronics to blossom into a viable industry.

Contacts: Curt Richter, 301-975-2082, Christina Hacker, 301-975-2233, or John Suehle, 301-975-2247

NanoBioTechnology for Single Cell and Single Molecule Manipulation and Measurement

Our work focuses on developing microfluidic systems and nanofluidic restrictions for cell and biomolecule transport and detection. We are interested in methods to pattern cells on surfaces, cell adhesion, sorting, and electronic and electro-chemical monitoring of cell activity. We are also interested in nanofluidic systems for DNA, RNA, and protein transport and detection to determine the structure and function. This project is part of a multidisciplinary program with collaborations in the NIST laboratories in Chemistry, Materials Science, Physics, and Biotechnology. Research would focus on the development of new fabrication methodologies, design and fabrication of new and novel nanofluidic systems, and measurement methods.

Contact: Michael Gaitan, 301-975-2070

Novel Test Structures for Char-acterizing the Performance of Advanced Multilevel Intercon-nection Systems

As the complexity of advanced integrated circuits continues to increase, new materials (copper, low-k dielectrics) need to be systematically characterized in order to perform parameter extraction for modeling on-chip interconnect systems at clock frequencies. The Enabling Devices ICs Group seeks individuals interested in developing new test structures, measurement methods, and analysis models needed to evaluate copper based, multilevel interconnection systems for high-frequency environments. Of particular importance are new methods for dimensional metrology, interfacial contact resistance, stress effects, median-time-to-failure, and high-frequency performance. In particular, we are interested in applying electrical parameters such as resistance and capacitance per unit length that are extracted by rf probing of strip-line test structures to the extraction of dimensional parameters such as CD and overlay.

Contact: Michael Cresswell, 301-975-2072

Optical and Physical Characterization of Thin Films Used in Integrated-Circuit Devices

The continued scaling of integrated-circuit (IC) technology requires more stringent precision and accuracy for the optical and physical measurements of thin films. Our research involves the development of optical measurement techniques, specifically spectroscopic ellipsometry, and internal photoemission and the enhancement of data analyses and modeling. Input from various physical, optical, and electrical techniques are needed to improve our knowledge of the electronic and optical properties of these thin films and their interfaces. With a broad collaboration from various thin-film measurement groups within NIST, our research will focus on relating the analyses of HRTEM, scanning probe methods, x-ray reflectance, Fourier-transform infrared, photo reflectance, Raman scattering, and various electrical techniques to improve our understanding of these films and also validate some of the optical models used in the analysis of the ellipsometric data. Simple actual IC devices can be fabricated in-house for electrical test structures.

Contacts: Curt Richter, 301-975-2082, or Nhan Nguyen, 301-975-2044

Organic Electronic Test Platforms

The NanoElectronic Device Metrology Project at NIST is addressing critical metrology issues associated with OFETs, one of the critical build-ing blocks for the emerging technology of organic electrics. The NEDM is developing OFET test structures and test methodologies to extract the fundamental electrical properties of organic semiconductors. This task is part of a large interdisciplinary team of physicists, chemists, engineers, and material scientists at NIST whose goal is to develop an integrated measurement platform to predict the performance of organic electronic devices based on composition, structure, and materials properties. The approach is to correlate the results of unique, world-class characterization techniques such as NEXAFS and cold-neutron scattering with the electrical behavior of OFET structures to determine the relationship between device performance and the structure, properties, and chemistry of critical materials and interfaces.

Contacts: David Gundlach, 301-975-2048, or Curt Richter, 301-975-2082

Organic Electronics

We are interested in organic-based electronic devices for use in large-area low-cost electronic applications, such as displays, radio frequency identification (RFID), and sensor arrays. Thin films of organic semiconductors, insulators, and conductors are used to fabricate integrated devices and circuitry, and it is expected that printing and inexpensive roll-to-roll processing will be developed to manufacture low-cost electronics on large-area flexible plastic substrates. The organic thin-film transistor (OTFT) is a core device since most electronic applications require active switches or circuitry. Although research on the OTFT has spanned nearly 20 years, we still lack a physically accurate, concise microscopic understanding of its electrical operation.

Developing predictive and physically-accurate models and theories is critical to establishing organic electronics as a mature and manufacturable technology. Core challenges hindering further development include (1) a poor understanding of the electronic structure at critical device interfaces; (2) a lack of detailed knowledge about defect generation, device reliability, and device lifetime; and (3) the extended use of in appropriate device structures, test methodologies, or models for extracting device parameters from measured electrical characteristics. The goal of this project is to solve these challenges by developing the appropriate electrical/optoelectrical characterization methods, test structures, and test methodology to quantitatively extract device properties and parameters, and to develop the microscopic models needed to describe the device operation and reliability.

Contact: David Gundlach, 301-975-2048

Physical and Electrical Properties of Advanced Gate Dielectric Films

It is increasingly difficult to characterize ultrathin gate dielectric films (typically 0.1 nm to 3.0 nm) used in metal-oxide-semiconductor (MOS) devices as technology drives them ever thinner. We are developing electrical test methods (using conventional techniques such as I-V and C-V, as well as low-temperature magnetotransport techniques) to measure the physical properties (e.g., film thickness and permittivity) of alternate gate dielectric materials such as high-k metal oxides as well as ultrathin SiO2. Electrical results are compared with those of optical and other measurement methods, and fundamental physical models are developed to be effective for more than one measurement technique. Because the interface between the dielectric film and the silicon substrate is critical to understanding these measurements, we are developing techniques to characterize buried interfaces (i.e., interface roughness) and are determining how the interface and physical properties affect device performance and reliability.

Contact: John Suehle, 301-975-2247

Physics of Semiconductor Devices and C and BN Nanotubes

Theoretical solid-state physics research for nanoelectronic applications is in progress in order to understand the operation of advanced electronic and molecular electronic devices and to provide more physically correct and numerically robust carrier transport models. Such transport models are used to interpret measurements and to enable predictive computer simulations of nano-electronic devices. For example, topics include densities of states, band structures, high-concentration effects, carrier lifetimes, and carrier mobilities. The approach involves careful experimental verification of the device models for elemental and compound semiconductors; for metallic, semiconducting, and insulating nanotubes; and for molecular electronics. We are interested in extending our theoretical research to include magnetic semiconductors (spintronics) such as manganese-doped GaAs, nanotubes, ultrathin nanolayers, and confined electrons and photons in semiconductor nanostructures.

Contact: Herbert Bennett, 301-975-2079

Reliability of Integrated Circuit Dielectric Films

Aggressive scaling of gate oxide thickness used in silicon integrated circuits necessitates the understanding of physical mechanisms responsi-ble for dielectric degradation and breakdown. We are particularly concerned with the reliability of ultrathin gate oxides that are in the direct tunnel-ing regime during circuit operation. Research focuses on (1) identifying parameters to deter-mine the physics of time-dependent dielectric breakdown of ultrathin dielectric films in the tunneling regime, (2) determining the effective-ness of highly accelerated stress tests to predict long-term reliability of thin dielectric films, (3) relating analytical characterization of oxide bulk and interfaces to electrical behavior, (4) identifying and controlling fabrication process parameters that affect intrinsic and extrinsic failure modes, and (5) characterizing and evaluat-ing alternate dielectrics for use as substitutes for silicon oxide in advanced circuit technologies.

Contact: John Suehle, 301-975-2247

Scanning Probe Metrology

We are developing scanning probe microscopes to characterize and manipulate the physical and electrical properties of electronic devices, semi-conductors, and related materials at the nanome-ter resolution scale. Projects are aimed at impact-ing silicon technology 5 to 10 years in the future or at characterization problems unique to com-pound semiconductors, molecular electronic devices, or quantum devices. We recently devel-oped scanning capacitance microscopy as a tool for measuring the two-dimensional dopant profile across a silicon p-n junction. We are particularly interested in projects to develop techniques to measure material properties in three dimensions and that have spatial resolution below 1-nm. Our interests extend to other scanning probe tech-niques, including variable temperature scanning tunneling microscopy in UHV, surface photo-voltage microscopy, and other optically pumped probes.

Contact: Joseph Kopanski, 301-975-2089

Silicon Building Blocks for Beyond-CMOS Circuits

The complementary-metal-oxide-semiconductor (CMOS) field-effect-transistor is showing fundamental limits associated with the laws of quantum mechanics and the limitations of fabri-cation techniques. This is driving research on innovative solutions to augment or replace CMOS technologies. Our goal is to develop the metrology that will enable emerging information processing technologies to extend electronic device performance improvements beyond the incremental scaling of CMOS. Quantum devices compatible with Si technologies such as silicon nanowires (Si-NW), resonant tunneling devices, and single-electron transistors, deliberately exploit quantum and size effects. We are devel-oping the electrical and physical metrology of the basic building blocks of these confined-silicon devices (e.g., quantum layers, wires, and quan-tum dots). Much of our focus has been on the fabrication of Si-NW FET devices. We are mak-ing and characterizing  top-down fabricated Si-NW FETs based on pushing the fabrication limits of silicon-on-insulator (SOI) technology as well as Si-NWs grown using CVD then positioned and contacted to form  bottom-up test structures and devices. Our interests include, but are not limited to fabrication, simulation, and characterization of device structures and constituent materi-als/processes. Our primary expectation is to be able to identify and address critical metrology issues for this emerging technology of silicon-based quantum devices.

Contact: Curt Richter, 301-975-2082

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Date created: 7/1/2005
Last updated: 8/14/2007